Position sensor for electromagnetic actuator

ABSTRACT

The present invention provides an accurate, non-contacting position sensor for an electromagnetic actuator. This position sensor includes a shaft to be detected ( 1 ), a first magnet ( 2 ) being fixed to the shaft ( 1 ) and having a first polarity vector ( 2   a ) parallel to an axis of the shaft ( 1 ), a second magnet ( 3 ) being disposed opposite to the first magnet ( 2 ) and having a second polarity vector ( 3   a ) crossing the first polarity vector ( 2   a ) substantially orthogonally three-dimensionally, and first and second semiconductor magnetoresistive elements ( 5   a   , 5   b ) being disposed over the second magnet ( 3 ) and functioning as a magnetoelectric transducer having a magnetosensitive axis substantially orthogonal to the first and second polarity vectors ( 2   a   , 3   a ). The first and second elements ( 5   a   ,5   b ) generates an output responsive to an axial movement of the shaft ( 1 ).

TECHNICAL FIELD

[0001] The present invention relates to a position sensor for anelectromagnetic actuator which is used in various systems for a vehicleand detects a position of a shaft to be detected which moves axially insynchronization with a movable shaft of the electromagnetic actuator.

BACKGROUND ART

[0002] To meet recently-increasing requirement for improving fuelefficiency of a vehicle, various measures directed toward theimprovement of the fuel efficiency have been studied. Among them, a highvoltage of a battery enables an electromagnetic actuator such as alinear solenoid or the like to have both a great driving force andminiaturization. Consequently, the electromagnetic actuator, whichhaving a higher efficiency to various kinds of electronics systems thana mechanical actuator, has been studied. In order to apply theelectromagnetic actuator to these electronics systems, the position of amovable shaft must be controlled accurately. Accordingly, a positionsensor becomes important for the accurate position detection of themovable shaft.

[0003] With reference to FIG. 7, a conventional position sensor(disclosed in Japanese Patent Laid-Open No.5-264326) for theelectromagnetic actuator will be hereinafter described.

[0004]FIG. 7(a) is a perspective general view of the conventionalposition sensor for the electromagnetic actuator.

[0005]FIG. 7(b) shows a cross section taken along arrow C-C of thesensor.

[0006]FIG. 7(c) is a perspective view detailing a relationship between amagnetoelectric transducer and a magnetic field generator of the sensor.

[0007] In FIGS. 7(a), 7(b) and 7(c), reference numeral 100 denotes ashaft to be detected. Reference numeral 100 a denotes a guide grooveformed in a longitudinal direction of the shaft 100. Reference numeral110 denotes a magnet 110 polarized magnetically in a thicknessdirection. Reference numeral 120 denotes a magnetic plate made of apermalloy shaped like an isosceles triangle. Reference numeral 130denotes a magnetic field generator including the magnet 110 and themagnetic plate 120 attached together in their respective longitudinaldirection matching together. Reference numeral 140 denotes amagnetoelectric transducer. Reference numeral 310 denotes a flat surfaceof the shaft 100. Reference numeral 320 denotes a slider including aninsulating material engages with the guide groove 100 a, for slidingsmoothly relative to the shaft 100. The magnetoelectric transducer 140provided at the slider 320 is mounted in parallel with the magneticfield generator 130 provided on the flat surface 310 of the shaft 100.

[0008] An operation of the conventional sensor will be explained below.

[0009] The shaft 100 is displaced relative to the slider 320 (in thedirection of an arrow D in FIG. 7(a)), the magnetic plate 120 is opposedto the magnetoelectric transducer 140 accordingly with various widths.Consequently, an electric field sensed by the magnetoelectric transducer140 varies in strength accordingly, thus enabling the sensor to detectthe position of the shaft 100.

[0010] The conventional position sensor described above, however, hasthe following problem. The conventional position sensor for theelectromagnetic actuator has a contacting portion functioning as a guidefor preventing the magnetoelectric transducer 140 from rotating about anaxis of the magnetic field generator 130. The sensor, if being used overa long period of time, has the contacting portion wearing unevenly andcausing backlash, which makes the sensor generate an unstable output.

DISCLOSURE OF THE INVENTION

[0011] The present invention addresses the problem discussed above andaims to provide a position sensor for an electromagnetic actuator. Theposition sensor is capable of accurate non-contacting positiondetection, not restricting rotation of a shaft to be detected about anaxis of the shaft.

[0012] To solve this problem, the position sensor of the presentinvention includes: a first magnet being fixed to the shaft to bedetected which moves axially in synchronization with a movable shaft ofthe electromagnetic actuator, and having a first polarity vectorparallel to the axis of the shaft; a second magnet being disposedopposite to the first magnet and having a second polarity vectorcrossing the first polarity vector substantially orthogonallythree-dimensionally; and a magnetoelectric transducer being disposedover the second magnet and having a magnetosensitive axis substantiallyorthogonal to the first and second polarity vectors. The magnetoelectrictransducer generates an output responsive to an axial movement of theshaft. With this configuration, the position sensor for theelectromagnetic actuator can detects the position accurately with nocontact, not restricting the rotation of the shaft about the axis of theshaft at all.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a sectional view of an electric EGR valve including aposition sensor for an electromagnetic actuator in accordance with anexemplary embodiment of the present invention.

[0014]FIG. 2 is a perspective view illustrating a principle of theposition sensor in accordance with the embodiment.

[0015]FIG. 3 is a sectional view illustrating a first magnet fixed to ashaft to be detected in accordance with the embodiment.

[0016]FIG. 4 is a cutaway view of an essential part of the positionsensor in accordance with the embodiment.

[0017]FIG. 5 illustrates an output characteristic of the position sensorin accordance with the embodiment.

[0018]FIG. 6(a) schematically illustrates a relationship between anoperation of the position sensor and an output voltage in accordancewith the embodiment, and

[0019]FIG. 6(b) schematically illustrates a relationship between theoperation of the sensor and an output voltage after a change intemperature.

[0020]FIG. 7(a) is a perspective view of a conventional position sensorfor the electromagnetic actuator,

[0021]FIG. 7(b) is a cross section taken along an arrow C-C of thesensor, and

[0022]FIG. 7(c) is a perspective view detailing a relationship between amagnetoelectric transducer and a magnetic field generator of the sensor.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] (Exemplary Embodiment 1)

[0024]FIG. 1 is a sectional view of an electric EGR valve including aposition sensor for an electromagnetic actuator in accordance with theexemplary embodiment of the present invention. FIG. 2 is a perspectiveview illustrating a principle of the position sensor in FIG. 1. FIG. 3is a sectional view illustrating a first magnet fixed to a shaft to bedetected in FIG. 2. FIG. 4 is a cutaway view of an essential part of theposition sensor in FIG. 1.

[0025] In FIGS. 1 to 4, reference numeral 1 denotes a shaft to bedetected which is shaped like a round bar and is made of non-magneticstainless steel such as austenitic heat-resisting steel (e.g. JIS-listedSUH-31B) or the like. Reference numeral 2 denotes a cylindrical firstmagnet made of SmCo rare earth magnet and being attached to the shaft 1coaxially with the shaft 1. Reference numeral 2 a denotes a firstpolarity vector indicating a direction of the magnetic polarity of thefirst magnet 2. Reference numeral 3 denotes a second magnet made of SmCorare earth magnet. Reference numeral 3 a denotes a second polarityvector indicating a direction of magnetic polarity of the second magnet3. Reference numerals 4 a and 4 b denote first and second magnetic fluxcollecting yokes, respectively. Reference numerals 5 a and 5 b denotefirst and second semiconductor magnetoresistive elements, respectively.Reference numerals 6 a and 6 b denote first and second fixed resistors,respectively. Reference numeral 17 denotes a gold wire. Referencenumeral 18 denotes a molded case. Reference numeral 19 denotes a leadframe. Reference numeral 20 denotes a relay board. Reference numeral 21denotes a relay terminal. Reference numeral 24 denotes a connectorterminal. Reference numeral 25 denotes a connector. Reference numeral 33denotes an armature. Reference numerals 34 denotes a first returnspring. Reference numeral 35 denotes a second return spring. Referencenumeral 36 denotes a first stator. Reference numeral 37 denotes a secondstator. Reference numeral 38 denotes a shaft. Reference numeral 39denotes a valve. Reference numeral 40 denotes an annular coil. Referencenumeral 41 denotes a valve base. Reference numeral 42 denotes arecirculation passage. Reference numeral 43 denotes a valve seat.Reference numeral 44 denotes an inner cover. Reference numeral 45denotes an outer cover. Reference numeral 46 denotes a first bearing.Reference numeral 47 denotes a second bearing. Reference numeral 51denotes an electric EGR valve. Reference numeral 52 denotes a positionsensor. Reference numeral 53 denotes a linear solenoid. Referencenumeral 54 denotes a valve mechanism.

[0026] The linear solenoid 53 includes: a vertically-movable armature 33fit into an internal cylindrical space formed with respective innerperipheral walls of first and second stators 36, 37 and the coil 40disposed between the lower and upper stators 36, 37; and the firstreturn spring 34 biasing the armature 33 upward. The first bearing 46 isfit into a center of the first stator 36. The shaft 38 is supported bythe bearing 46 to be vertically slidable and movable integrally with thearmature 33 with an upper end of the shaft 38 secured to a center ofarmature 33.

[0027] A lower end of the shaft 38 is formed into the valve 39. In thevalve base 41 of the valve mechanism 54, the recirculation passage 42for exhaust gas is formed. The valve seat 43 is positioned at a midpointof passage 42 within valve base 41, and the valve 39 provided at thelower end of the shaft 38 is seated on and unseated from the valve seat43 to selectively close and open.

[0028] The shaft 1 supported in vertically movable protrudes into acenter of the linear solenoid 53 with a lower end of the shaft 1contacting with the armature 33.

[0029] The second return spring 35 biases the shaft 1 including thefirst magnet 2 mounted thereto downward and is held by the inner cover44. The inner cover 44 and an electrical connecting portion between therelay terminal 21 and the connector terminal 24 are covered with theouter cover 45.

[0030] In FIG. 2, an axis of the shaft 1 is parallel to the firstpolarity vector 2 a of the first magnet 2. The second magnet 3 isdisposed opposite to the first magnet 2. The first and second polarityvectors 2 a, 3 a cross to each other substantially at right anglesthree-dimensionally. The first and second magnetic flux collecting yokes4 a, 4 b each made of a magnetic sheet are disposed over opposed sidesof second magnet 3, respectively, and are disposed perpendicularly tothe second polarity vector 3 a of-the second magnet 3. The first andsecond semiconductor magnetoresistive elements 5 a, 5 b are disposedover respective sides of the yokes 4 a, 4 b. A magnetosensitive axis ofthe first and second magnetoresistive elements 5 a, 5 b is orthogonal tothe first and second polarity vectors 2 a, 3 a. The first and secondmagnetoresistive elements 5 a, 5 b and first and second fixed resistors6 a, 6 b are electrically connected to form a Wheatstone bridge.

[0031] Regarding dimensions of the essential parts shown in FIG. 2, thesecond magnet 3 has a length along the second polarity vector 3 a of 4mm, a length in parallel with the shaft 1 of 5 mm, and a lengthperpendicular to the shaft 1 of 4 mm. Each of the first and second yokes4 a, 4 b has a thickness of 10 mm. The first magnet 2 has an outsidediameter of φ8 mm and an axial length of 12 mm. The distance between anouter peripheral surface of the first magnet 2 and a surface of thefirst magnetoresistive element 5 a as well as the distance between theouter peripheral surface of the first magnet 2 and a surface of thesecond magnetoresistive element 5 b is 2.8 mm.

[0032] In FIG. 3, the first magnet 2 is made of resin paste includingthe SmCo rare earth magnet and is insert-molded into a pipe 1 a. Aprojection 1 b provided at the pipe 1 a prevents the pipe from gettingout. The pipe 1 a is press-fit to the shaft 1.

[0033] In FIG. 4, the first and second semiconductor magnetoresistiveelements 5 a, 5 b are die-bonded to the lead frame 19, and electrodes(not shown) disposed over magentoresistive elements 5 a, 5 b arewire-bonded to the lead frame 19 by a gold wire 17. These components aresubjected to transfer molding, so that molded case 18 is formed over thefirst and second magnetic flux collecting yokes 4 a, 4 b and the secondmagnet 3. The lead frame 19 is electrically coupled to the relayterminal 21 via the relay board 20. These components are covered with asealing resin 22. As shown in FIG. 1, the relay terminal 21 iselectrically connected to the connector terminal 24, and connector 25outputs a signal.

[0034] An operation in accordance with the present embodiment will behereinafter described.

[0035] In the electric EGR valve 51, a current input from a control ECU(not shown) to the coil 40 varies, the shaft 38 moves accordingly.Consequently, an opening of the valve 39 as well as an amount of exhaustgas recirculated varies accordingly. Simultaneously, the moving shaft 38moves the shaft 1 of the position sensor 52, and the first magnet 2mounted to the shaft 1 moves accordingly. This changes a strength of amagnetic field applied to the first and second magnetoresistive elements5 a, 5 b disposed over the respective sides of the yokes 4 a, 4 bdisposed over the respective opposed sides of the second magnet 3perpendicularly to the second polarity vector 3 a of the second magnet 3opposite to the first magnet 2. The variance of the magnetic fieldstrength get respective resistances of the magnetoresistive elements 5a, 5 b to vary. The Wheatstone bridge formed with the first and secondmagnetoresisitive elements 5 a, 5 b and the first and second fixedresistors 6 a, 6 b converts the resistance changes into a change involtage.

[0036]FIG. 5 illustrates an output of the position sensor 52 describedin above. The horizontal axis of FIG. 5 represents a displacement of thefirst magnet 2 about a reference center of the second magnet 3 in aparallel direction with the shaft 1 of the second magnet 3, and thevertical axis represents an output voltage of the position sensor 52.The output voltage varies linearly with the displacement of the firstmagnet 2. When the displacement changes from −5 mm to +5 mm, the outputvoltages ranges in a large value, 1V or more.

[0037] The moving amount of the shaft 38 corresponds to the opening ofthe valve 39, and the detected opening is fed back to the ECU forcontrol. The movement of the shaft 38 is restricted by the armature 33including the shaft 38 secured thereto, and the first and secondbearings 46, 47. In other words, the valve 39 is located at afully-closing position (corresponding to a displacement of +4 mm in FIG.5) when the armature 33 contacts with the bearing 47, and is located ata fully-opening position (corresponds to a displacement of −4 mm in FIG.5) when the armature 33 contacts with the bearing 46.

[0038] A relationship between such operating pattern and the outputvoltage is shown schematically in FIG. 6(a). In FIG. 6(a), referencesymbol Vc denotes an output voltage (corresponding to 3.0V in FIG. 5)representing the fully-closing position, reference symbol Vo denotes anoutput voltage (corresponding to 2.0V in FIG. 5) representing thefully-opening position, and reference symbol V denotes the presentoutput voltage.

[0039] A present actual valve position X based on FIG. 6(a) can beexpressed as:$X = \frac{\left( {V - {V\quad o}} \right) \times 1s\quad t\quad r\quad o\quad k\quad e}{{V\quad c} - {V\quad o}}$

[0040] With the above-mentioned configuration, a temperature drift ofthe output voltage resulting from a temperature change occurs as shownin FIG. 6(b). In FIG. 6(b), reference symbol Vc1 denotes an outputvoltage representing the fully-closing position after the temperaturedrift, reference symbol Vo1 denotes an output voltage representing thefully-opening position after the temperature drift, and reference symbolV1 denotes the present output voltage after the temperature drift.

[0041] Even if the temperature changes, the present actual valveposition X can be obtained by the equation:$X = \frac{\left( {{V1} - {V\quad {o1}}} \right) \times 1s\quad t\quad r\quad o\quad k\quad e}{{V\quad {c1}} - {V\quad {o1}}}$

[0042] In the present embodiment, the first and second magnets 2, 3 andthe first and second magnetic flux collecting yokes 4 a, 4 b basicallyform a substantially-closed magnetic circuit hardly affected by anexternal magnetic field.

[0043] In this embodiment, the distance between the outer peripheralsurface of the first magnet 2 and the surface of the first semiconductormagnetoresistive element 5 a as well as a distance between the outerperipheral surface of the first magnet 2 and the surface of the secondsemiconductor magnetoresistive element 5 b is 2.8 mm. However, thedistance ranging from 2.5 mm to 3.1 mm ensures the same effect.

[0044] In this embodiment, the position sensor 52 is providedindependently upon the linear solenoid 53 and valve mechanism 54. Thisfacilitates replacing the position sensor 52 having an problem evenduring being manufactured. Also, even if the shaft 1 rotates about itsaxis, the sensor detects the position accurately. This is because thefirst magnet 2 is cylindrical and coaxial with the shaft 1, and thespace between the first and second magnetoresistive elements 5 a, 5 bremains invariable. Further, the sensor detects the position accuratelysince the first and second magnets 2, 3 employs the SmCo rare earthmagnet hardly having a magnetic force hardly changing due to thetemperature change or due to a decline of durability.

[0045] According to the present embodiment, an amplifier for the outputof the position sensor 52 is not employed. However, the output may comeout through the amplifier. This is applicable to cases where a processorin the subsequent stage requires a signal voltage reaching a specifiedor higher input level. The amplifier may be an AC amplifier. The ACamplifier is applicable to detecting the position of the shaft 1 movingat a specified or higher frequency. Thus, the system has an advantagethat the temperature drift affecting the first and second semiconductormagnetoresistive elements 5 a, 5 b can be cancelled for more accuratedetection.

[0046] A bare chip, functioning as the amplifier, and the first andsecond semiconductor magnetoresistive elements 5 a, 5 b may be packagedinto one by being die-bonded to the lead frame 19 and wire-bonded by agold wire 17. Consequently, the wiring between the first and secondmagnetoresistive elements 5 a, 5 b and the bare chip is reduced, thusimproving noise immunity. In addition, a circuit board can have areduced area since requiring little external circuitry, thus allowingthe sensor to be small.

[0047] In the present embodiment, the electric EGR valve to which theposition sensor is applied is described. However, the position sensor ofthe present invention is applicable to various devices each including asolenoid-valve-driving device and the like employing an electromagneticactuator.

[0048] In the solenoid-valve-driving device, the valve and the valveseat wear due to a repeated use over a long period of time, so that theseating position of the fully-closing valve changes. Even in this case,the device, upon monitoring the output voltage of the position sensor atthe fully-closing position, utilizing the voltage as information usefulfor diagnosis.

[0049] In the present embodiment, the semiconductor magnetoresistiveelements is used as a magnetoelectric transducer, but themagnetoelectric transducer is not limited to it, and may employ, forexample, a Hall element.

[0050] In this embodiment, the magnetic flux collecting yokes 4 a, 4 beach made of a sheet made of the magnetic material are disposed over therespective opposed sides of the second magnet 3 and disposedperpendicularly to the second polarity vector 3 a. The first and secondsemiconductor magnetoresistive elements 5 a, 5 b is disposed over therespective sides of the yokes 4 a, 4 b with the magnetosensitive axis ofthe elements 5 a, 5 b substantially orthogonal to the first and secondpolarity vectors 2 a, 3 a. However, the present invention is not limitedto this example. For example, the first and second semiconductormagnetoresistive elements 5 a, 5 b functioning as the magnetoelectrictransducer may be disposed over the second magnet 3 with respectivemagnetosensitive axis thereof substantially orthogonal to the first andsecond polarity vectors 2 a, 3 a. In this case, it is preferable thateach of first and second magnetoresistive elements 5 a, 5 b is disposedover an end of the second magnet 3 for its output sensitivity.

INDUSTRIAL APPLICABILITY

[0051] According to the present invention, as explained above, aposition sensor for an electromagnetic actuator detects a positionaccurately with no contact, while not restricting the rotation of ashaft thereof to be detected about the axis of the shaft at all.

What is claimed is:
 1. A position sensor for an electromagnetic actuator, comprising: a shaft to be detected moving axially in synchronization with a movable shaft of the electromagnetic actuator; a first magnet fixed to said shaft to be detected, said first magnet having a first polarity vector parallel with an axis of said shaft to be detected; a second magnet disposed opposite to said first magnet, said second magnet having a second polarity vector crossing said first polarity vector substantially orthogonal three-dimensionally; and a magnetoelectric transducer disposed over said second magnet, said magnetoelectric transducer having a magnetosensitive axis substantially orthogonal to said first and second polarity vectors; wherein said magnetoelectric transducer generates an output responsive to an axial movement of said shaft to be detected.
 2. The position sensor of claim 1, wherein said first magnet is cylindrical and coaxial with said axis of said shaft to be detected.
 3. The position sensor of claim 1, wherein said magnetoelectric transducer includes first and second semiconductor magnetoresistive elements disposed over said second magnet and aligned in parallel with said second polarity vector.
 4. The position sensor of claim 3, further comprising an amplifier provided between said first and second semiconductor magnetoresistive elements.
 5. The position sensor of claim 1, wherein each of said first and second magnets made of SmCo rare earth magnet.
 6. The position sensor of claim 1, wherein said shaft to be detected is made of non-magnetic material.
 7. A position sensor for an electromagnetic actuator, comprising: a shaft to be detected moving axially in synchronization with a movable shaft of the electromagnetic actuator; a first magnet fixed to said shaft to be detected, said first magnet having a first polarity vector parallel with an axis of said shaft to be detected; a second magnet disposed opposite to said first magnet, said second magnet having a second polarity vector crossing said first polarity vector substantially orthogonally three-dimensionally; two magnetic flux collecting yokes disposed over respective opposed sides of said second magnet and disposed perpendicularly to said second polarity vector, said magnetic flux collecting yokes being made of magnetic material; and magnetoelectric transducers disposed over respective sides of said magnetic flux collecting yokes, said magnetoelectric transducers each having a magnetosensitive axis substantially orthogonal to said first and second polarity vectors, wherein said magnetoelectric transducers generate outputs responsive to an axial movement of said shaft to be detected.
 8. The position sensor of claim 7, wherein said magnetoelectric transducers include first and second semiconductor magnetoresistive elements disposed over said respective sides of said magnetic flux collecting yokes, said first and second semiconductor magnetoresistive elements being aligned in parallel with said second polarity vector. 